The material selected for a food packaging tray must be economical to produce. The cost of such a tray must not comprise a significant portion of the total cost of the packaged food product. Cost considerations place important constraints upon suitable materials which may be used for trays.
A suitable tray must also be durable and resistant to breakage. Meat products, and other food products, are typically subjected to rough handling during the course of their transportation from the packaging plant to the distributor, then to a retail outlet, and then to a consumer's home for final consumption. Several food packages are typically bound together in a single box, because it would be too slow and inconvenient to handle each package individually. The relatively heavy weight of such boxes sometimes results in a requirement that the boxes be handled by machinery. If such boxes are handled manually, they are often dropped or thrown. Successful testing of a packaging tray requires testing in the field by subjecting the tray to actual handling conditions through a normal distribution route to test the surviability of the tray. A suitable tray must be able to survive such handling.
In the past, Styrofoam has been used for trays. Styrofoam has proven to be less than completely satisfactory because of its brittleness and susceptibility to breakage. Some food products, especially meat, are relatively heavy and require additional strength from a packaging tray, which may not be available with Styrofoam.
In the past, cardboard has been used for trays. A suitable tray must be able to survive for the relatively long period of time that may elapse between packaging and final consumption of the food products. The juices from many foods, especially meat, commonly saturate a cardboard tray. The strength of the cardboard tray quickly deteriorates when the material is saturated. For this reason, cardboard is less than satisfactory as a tray material.
A suitable tray must be designed so that it can accept a cellophane wrapping around the tray and the food. It is important that the tray be designed so that it will not tear the cellophane wrapping during extensive handling and transportation. To prevent tearing of the cellophone, the design of the corners of the tray can be critical.
While strength must be maintained in a tray, the tray must also be flexible. Lack of flexibility can present problems in sealing the cellophane film on the bottom of the tray.
A food tray must be manufactured from materials which may maintain direct contact with the food substance without adverse health affects, or adverse effects on the taste and odor of the food. The material must be noncontaminating, even after prolonged contact with the food or meat which is packaged. The material must maintain its strength even in a deep chill environment. The material must have a low thermal coefficient to reduce the amount of energy required to lower the temperature of the tray itself when chilling the food product. The tray material should preferably be suitable for use in a microwave oven environment.
The weight of the tray is also an important factor. The weight of the tray adds to the weight of the food product which must be shipped after the product has been packaged. For a tray that weighs one ounce more than others, use of the tray could result in approximately 1,000 pounds additional weight per truckload of meat, assuming a typical truckload comprising 16,000 trays and a 36,000 pound load. The weight of the trays must be minimized, as the additional weight increases the transportation costs for transporting the packaged food product.
Impact polypropylene materials have been available, but have not had the impact strength required, or else lack the molding characteristics needed to produce a flat tray. The materials used for a food tray must not contribute any undesirable odor or taste to the food product. Conventional plastics typically have one or both of these disadvantages.
Efforts in the past to achieve a tray for packaging food products, especially meat, which has all of the characteristics of high strength, low weight, low temperature coefficient, adequate molding characteristics to produce a flat tray, and low microwave absorption, while still remaining within cost constraints, have not been altogether satisfactory. The problems enumerated above are not intended to be exhaustive, but are illustrative of problems in the prior art which are addressed by the present invention.